Reader-printer

ABSTRACT

Disclosed is a reader-printer capable of being changed over between a reader mode in which the light image of an original is projected onto a screen and a printer mode in which the light image of the original is projected onto a photosensitive medium. The reader-printer has first optical means for forming a first optical path for projecting the light image onto the screen and second optical means for forming a second optical path for projecting the light image onto the photosensitive medium. The second optical means includes a first mirror and a second mirror. The first mirror is movable so that it is positioned outside the first optical path during the reader mode and is positioned in the first optical path during the printer mode. The second mirror is movable with the first mirror. When the first mirror is being moved between a first position and a second position, the light from the original is detected by light detecting means, and when the first mirror is positioned in the first optical path, the light image is reflected by the first mirror and then reflected and guided to the photosensitive medium by the second mirror.

This is a continuation of application Ser. No. 483,122, abandoned, filedApr. 8, 1983.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a reader-printer changeable over between areader mode in which the light image of an original is projected onto ascreen for observation and a printer mode in which the light image ofthe original is projected onto a photosensitive medium by a slitexposure system and the copy image thereof is obtained.

2. Description of the Prior Art

In the reader-printer of this type, it has heretofore been practisedthat the reader optical path for projecting the image of an originalsuch as a microfilm onto a screen and the printer optical path forprojecting the image of the original onto a photosensitive medium areused partly in common with each other. To change over the apparatusbetween the reader mode and the printer mode, a change-over mirror isprovided in the common optical path and by rotating this mirror, it isplaced into and out of the optical path to thereby effect thechange-over between the two modes. This change-over method has requireda driving device for rotating the change-over mirror, and this has ledto the complexity of the construction of the apparatus as well as thebulkiness of the change-over mirror which is attributable to thenecessity of reflecting the entire image and thus, it has been difficultto make the apparatus compact. Further, it is difficult to accuratelydispose the rotatable mirror at a predetermined angle in the commonoptical path and, even if such mirror is accurately disposed, frequentchange-over operation may derange the disposition angle of the mirrorwith a result that the image cannot be accurately projected onto apredetermined position.

Also, in a reader-printer wherein the copying operation is effected by aslit exposure system, it is necessary to move a scanning member to scanthe original and this leads to the necessity of providing a seconddriving device for moving the scanning member and thus, the conventionalreader-printer has been provided with the device for driving thechange-over mirror and the device for driving the scanning member. Thishas led to the complexity, bulkiness and expensiveness of the apparatus.

Generally, originals to be copied in a copying apparatus include thoseof high contrast such as printed matter and those of low contrast suchas newspaper or diazo copies, and to obtain good copies, it is necessaryto change the exposure amount by the exposure lamp or the bias voltageof the developing device. In such case, the density of the original isdetected and the exposure amount, etc. are controlled in accordance withthe detected density. The detection of the image density of the originalis accomplished by detecting the light reflected by or transmittedthrough the whole or part of the original, and in such photometricsystem, when for example a document is to be copied, even if thecharacters on the document are of the same density, the photometricvalue (the quantity of light received) may differ depending on theportion which the characters occupy in the photometrically measured area(which corresponds to the light-receiving area of the light-receivingelement) and thus, the quality of the detected copy image varies inconformity with the size of the photometrically measured area. Toaccurately detect the image density, photometry can be effected by alight-receiving element of a small light-receiving area, but in thiscase, it is necessary to provide a number of light-receiving elements toreliably detect the ground density of the original and the density ofthe images such as characters, and the increased number oflight-receiving elements leads to an increased number of attendantcircuits (for example, an output amplifying circuit, a photometric valuedetecting circuit, etc.) and accordingly complexity and expensiveness ofthe apparatus.

SUMMARY OF THE INVENTION

It is an object of the present invention to eliminate the above-noteddisadvantages.

It is another object of the present invention to provide areader-printer which is simple and compact in construction.

It is still another object of the present invention to provide areader-printer which is capable of being simply and quickly changed overbetween a reader mode and a printer mode.

It is yet still another object of the present invention to provide areader-printer in which the change-over operation between the readermode and the printer mode and the scanning operation for slit exposurecan be simply accomplished by a common driving means.

It is a further object of the present invention to detect the density ofan original during the aforementioned change-over operation and obtain aproper copy image on the basis of the detected density.

It is still a further object of the present invention to simply detect awide range of density of originals and obtain a proper copy image on thebasis of the detected density. These objects of the present inventionwill become fully apparent from the following detailed descriptionthereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the construction of a reader-printer to whichthe present invention is applied.

FIGS. 2 and 3 illustrate the operative condition of the reader-printershown in FIG. 1.

FIG. 4 is a perspective view of the slit plate.

FIGS. 5, 6 and 7 illustrate the detection areas of a light-receivingelement.

FIG. 8 is a perspective view showing a mechanism for moving scanningmirrors.

FIG. 9 shows another embodiment of the scanning mirrors.

FIG. 10 is a perspective view showing another embodiment of the slitplate.

FIG. 11 is a block diagram of an exposure control circuit.

FIG. 12 illustrates the phase control system.

FIGS. 13 and 14 are flow charts of the program for carrying out thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will hereinafter be described with respect to specificembodiments thereof shown in the drawings. Referring to FIG. 1 whichshows a copying apparatus to which the present invention is applied, anoriginal such as a microfilm 1 is illuminated by an illuminating devicecomprising an illuminating lamp 2, a spherical mirror 3 and a condenserlens 4. The entire image in one frame of the microfilm 1 is projectedonto a screen 8 by a projection lens 5 via stationary mirrors 6 and 7disposed at predetermined positions. The lens 5 and mirrors 6 and 7together form a first optical path for projecting the images on the film1 onto the screen 8.

Designated by 10 and 11 are scanning mirrors for scanning theimage-bearing surface of the film 1 to slit-expose a photosensitive drum12 to the optical images of the film. The reflecting surfaces of themirrors 10 and 11 form an angle of 90°. The first and second mirrors 10and 11 are reciprocated integrally, i.e. as a unit, in the directions ofarrows B and B', and the first mirror is placed in a first optical pathduring the printer mode. When the first mirror 10 is placed in the firstoptical path, the first and second mirrors form a second optical pathfor projecting the images of the film onto the photosensitive drum 12.The photosensitive drum 12 is connected to a motor, not shown, and isrotated at a predetermined velocity in the direction of arrow A. Thefirst and second mirrors 10 and 11 are fixedly supported by a supportmember 13 which is coupled to a drive source and is rectilinearlyreciprocated in the directions of arrows B and B' while holding thescanning mirrors 10 and 11. The movement velocity of the scanningmirrors 10 and 11 is set to 1/2 of the peripheral velocity V of thephotosensitive drum 12, this movement velocity V/2 being constantirrespective of the projection magnification. The scanning mirrors 10and 11 each have an elongated shape which projects a slit-like area ofthe entire image in one frame of the microfilm onto the photosensitivedrum 12. The scanning mirrors 10 and 11 are moved together in adirection across the optical path of the lens 5 (a directionperpendicular to the optical axis of the lens) in synchronism withrotation of the photosensitive drum 12, whereby the entire image in oneframe of the microfilm to be copied is successively scanned andprojected in a slit-like form onto the photosensitive drum 12.

When the apparatus is in the reader mode, the first and second mirrors10 and 11 are placed at their normal position (first position) shown inFIG. 1, and when the first mirror 10 lies outside the optical path ofthe lens 5 (first optical path), the images of the microfilm 1illuminated by the lamp 2 are projected onto the screen 8 via thestationary mirrors 6 and 7, whereby these images can be viewed on thescreen.

On the other hand, when the apparatus has been changed over from thereader mode to the printer mode, the support member 13 is moved in thedirection of arrow B, whereby the first and second mirrors 10 and 11 aremoved to their position as shown in FIG. 2 and thus, the first mirror isplaced at the exposure starting position (second position) in the firstoptical path. When the first mirror 10 is placed at the exposurestarting position, the support member 13 is moved in the oppositedirection, namely, the direction of arrow B' and, during the movementthereof in the direction of arrow B', the images of the film areprojected onto the photosensitive drum 12 via the first and secondmirrors and a slit plate 14, whereby the images are scanned for exposureon the photosensitive drum, thus completing the exposure scanning in thecondition of FIG. 3. After the completion of the image exposure, thesupport member 13 is continuedly moved in the direction of arrow B' and,when the first and second mirrors 10 and 11 have returned to theirnormal position shown in FIG. 1, the support member 13 is stopped,whereby the apparatus is automatically changed over from the printermode to the reader mode. When it is desired to obtain a number ofcopies, the scanning mirrors 10 and 11 may be reciprocated between theexposure starting position and the exposure terminating position asoften as required.

In the above-described embodiment, the scanning mirrors 10 and 11 aremoved in the same direction, but alternatively they may be moved indifferent directions. Also, the scanning mirror 10 is moved in adirection perpendicular to the optical axis of the lens, butalternatively it may be moved in a different direction to scan theimage.

The photosensitive drum 12 comprises a three-layer photosensitive mediumcomprising a conductive layer, a photoconductive layer and a transparentinsulating layer laminated in the named order, and has the insulatinglayer on the surface thereof. This photosensitive drum is uniformlycharged by a primary charger 50, and then has the primary charge removedtherefrom by an AC discharger or a DC discharger 51 opposite in polarityto the primary charger 50 while being exposed to the image light fromthe microfilm, whereafter it is uniformly exposed to the light from alamp 52, whereby an electrostatic latent image corresponding to theprojected image pattern is formed on the surface of the photosensitivedrum. The electrostatic latent image on the photosensitive drum 12 isthen developed by a developing device 53, whereafter the developed imageis transferred to transfer paper 56, fed from a cassette 55, by an imagetransfer device 54.

In FIG. 1, reference numeral 60 designates a position detector fordetecting the position of the support member 13. The position detector60 is disposed along the movement path of members 61a, 61b and 61c to bedetected which are provided at predetermined locations on the supportmember 13. The detector 60 comprises a photoelectric conversion elementand a lamp, and the members 61a-61c to be detected each comprise anopaque projection. When the support member 13 is moved, the optical pathpassing through the photoelectric conversion element and the lamp of thedetector 60 is intercepted by the members 61a-61c to be detected and,when this optical path is intercepted, the detector 60 detects themembers to be detected and puts out a signal. A shutter, not shown, isprovided in a second optical path and is operable by the output signalof the detector 60.

When the apparatus is in the reader mode, the detector 60 detects themember 61a to be detected and, at this time, the first mirror 10 is inits normal position shown in FIG. 1. When the apparatus is changed overto the printer mode and the detector 60 detects the member 61c to bedetected, the first mirror 10 is in the scanning starting position shownin FIG. 2, and when the detector 60 detects the member 61b to bedetected, the first mirror 10 is in the scanning terminating positionshown in FIG. 3.

The detector 60 controls drive means for moving the support member 13.When the apparatus has been changed over from the reader mode to theprinter mode, said drive means drives to move the support member 13 inthe direction of arrow B, and when the detector 60 detects the member61c to be detected during this movement, the drive means is stopped by asignal put out from the detector 60, and then the drive means drives inthe reverse direction to move the support member 13 in the direction ofarrow B' and thereafter, when the detector 60 detects the member 61a tobe detected, the drive means is stopped by a signal put out from thedetector 60 and thus, the apparatus assumes the reader mode again. Whenthe detector 60 detects the member 61b to be detected during themovement of the support member 13 in the direction of arrow B', theexposure of the photosensitive drum 12 is terminated.

Referring now to FIG. 8 which shows a scanning mirror driving unit, thesupport member 13 has side plates 70 and 71 and sloping plates 72 and 73fixed to the side plate 70. The first mirror 10 is fixed to the slopingplate 72 and the second mirror 11 is fixed to the sloping plate 73 at anangle of 90° with respect to the first mirror 10. The side plate 71 hasfixed thereto slidable bearings 75 and 76 which are slidably mounted ona fixed shaft 77. Likewise, the side plate 70 has fixed thereto slidablebearings (not shown) which are slidably mounted on a fixed shaft 78.Thus, the side plates 70, 71 and sloping plates 72, 73 are reciprocallymovable along the fixed shafts 77, 78 in the directions of the arrows.The intermediate portion of wire 81 is wound on a drive pulley 80 andone end of the wire 81 is wound on pulleys 82 and 83 rotatably supportedon the fixed portion of the apparatus body and is secured to the bearing75, while the other end of the wire is wound on pulleys 84 and 85rotatably supported on the fixed portion of the apparatus body and issecured to the bearing 76.

The drive pulley 80 is connected to a motor, not shown, for rotation inforward and reverse directions and, by rotation of the drive pulley 80,the left half or the right half of the wire 81 is rolled up while theright half or the left half of the wire is rewound, whereby the supportmember 13 and accordingly the mirrors 10 and 11 are moved to left orright at a predetermined velocity, thus effecting the change-overbetween the reader mode and the printer mode as well as the scanningduring the printer mode.

Referring to FIG. 4 which shows a slit unit, a slit plate 14 has a slit14a therein and is supported by a guide shaft 15 for reciprocal movementin the directions of arrows C and C', one end of the slit plate beingfixed to an endless wire 18 wound on pulleys 16 and 17. A roller 19 ismounted on the other end of the slit plate 14 and movement of the slitplate may cause the roller 19 to roll on the rail (not shown) of theapparatus body. The pulley 16 is coupled to a drive source (motor) formoving the support member 13 and the slit plate 14 is designed to bemoved in synchronism with movement of the scanning mirrors 10 and 11.The reason why the slit plate 14 is moved is that because the incidentangle of the light ray reflected by the second mirror 11 during theprinter mode and incident on the photosensitive drum 12 varies inaccordance with the movement of the first and second mirrors, the slitplate is moved correspondingly to the variation in said incident angle,thereby making the quantity of light passed through the slit 14aconstant irrespective of the position of the second mirror. The amountof movement of the slit plate 14 is very small as compared with theamount of movement of the scanning mirrors 10 and 11. The pulley 16 isrotatable in forward and reverse directions by the drive source and theslit plate 14 is reciprocally moved by the rotation of the pulley 16.

A light-receiving element 20 for detecting the image density of theoriginal is disposed on a movable plate 21 which in turn is movablydisposed on the slit plate 14, and it is adjacent to the slit 14a. Themovable plate 21 may be moved with the light-receiving element 20 in thedirections of arrow E by wire 22, whereby the light-receiving element 20may be moved in a direction perpendicular to the original scanningdirection (direction B). One end of the wire 22 is connected to a coilspring 23 fixed at one end to the slit plate 14, and the other end ofthe wire 22 is secured to the apparatus body, so that as the slit plate14 is moved, the coil spring 23 expands or contracts through theintermediary of the wire 22, whereby the movable plate 21 isreciprocally moved in the directions of arrow E. A roller 24 is providedon the movable plate 21 and is loosely fitted in a groove rail 25 formedin the slit plate 14, so that movement of the movable plate 21 may causethe roller 24 to roll along the groove rail 25. The light-receivingelement comprises a known photoelectric conversion element whoselight-receiving area is small, and detects the quantity of light fromthe original. The detection signal of the light-receiving element issupplied through a flexible electric cord 26 to a lamp control circuit29, which controls the brightness of the lamp 2 on the basis of thephotometric value measured by the light-receiving element 20 so thatthere may be obtained an optimum exposure amount corresponding to thedensity of the original.

The detection of the image density by the light-receiving element takesplace prior to the regular exposure step. In the present embodiment, thelight-receiving element 20 receives the light from the originalreflected by the mirrors 10 and 11 while these mirrors are being movedfrom their normal position to the exposure starting position during thechange-over from the reader mode to the printer mode, and the electricpower supplied to the lamp 2 is adjusted in conformity with the maximumand minimum luminous intensities of the light received by thelight-receiving element 20, whereby the lamp is adjusted to anappropriate quantity of light and then the regular exposure scanningtakes place. In the present embodiment, when a copy switch is closed,the lamp 2 is turned on and as the preparatory scanning, the scanningmirrors 10, 11 and slit plate 14 are moved in the direction of arrow Bin synchronism with each other and thus, the apparatus is changed overfrom the reader mode to the printer mode. During this preparatoryscanning, the light-receiving element 20 is moved in a directionperpendicular to the original scanning direction, namely, a directionparallel to the slit 14a (direction E) in synchronism with the movementof the slit plate 14, thereby photometrically scanning the original.After a predetermined range of the original has been photometricallyscanned, the brightness of the lamp 2 is adjusted on the basis of themaximum and minimum of the photometric value, whereby the brightness ofthe lamp 2 is set to an appropriate condition corresponding to thedensity of the original and thereafter, the scanning mirrors 10, 11 andslit plate 14 come to assume the predetermined exposure startingposition. The movement velocity of the scanning mirrors during thepreparatory scanning may be made higher than the movement velocity ofthe mirrors 10 and 11 during the regular exposure scanning to therebyreduce the time required. Also, the quality of the copy image may beadjusted by adjusting the exposure time, the aperture, the bias voltageof the developing device, etc. on the basis of the photometric valuemeasured by the light-receiving element. When the preparatory scanningis terminated with the mirrors 10 and 11 placed at the exposure startingposition, the mirrors 10 and 11 are moved forwardly in the direction ofarrow B' in synchronism with rotation of the photosensitive drum 12 andthe regular exposure scanning is effected.

Referring now to FIG. 5 which shows the area of the originalphotometrically measured by the light-receiving element, referencenumeral 35 designates the image of the original to be copied. When thescanning mirrors 10 and 11 scan the image 35 in the direction of arrow Band the light-receiving element 20 is moved in the direction of arrow Eby an amount corresponding to the length of the arrow, thelight-receiving element 20 has photometrically measured the image areaindicated by a straight line 38 having a certain width. Accordingly, thelight-receiving element 20 has photometrically scanned obliquely thesurface of the original and thus, the densities of the character portionand the ground portion of the original can be detected accurately andreliably. Also, in FIG. 6, if the light-receiving element 20 is movedforwardly, backwardly and again forwardly as indicated by arrows Eduring the movement of the scanning mirrors 10 and 11 in one directionduring the preparatory scanning, the light-receiving element 20 hasphotometrically measured the image area indicated by a curve 40 having acertain width and thus, the density of the image can be widely detectedsimply by the use of a single light-receiving element.

In the present invention, the number of light-receiving elementsprovided may be one or more.

FIG. 7 shows the photometrically measured area in a case where twolight-receiving elements provided in spaced apart relationship with eachother in a direction perpendicular to the direction of movement of thescanning mirrors are moved forwardly in the direction of arrow E duringthe movement of the mirrors 10 and 11 in one direction. The image areaindicated by straight lines 42 is photometrically measured by the twolight-receiving elements.

In the embodiment illustrated, the light-receiving elements are moved inthe direction perpendicular to the direction of movement of the scanningmirrors, but alternatively they may be moved in a direction intersectingor non-parallel to the direction of movement of the scanning mirrors.

Also, the light-receiving elements may be directly moved by a motor orthe like. Further, the position at which the light-receiving elementsare disposed is not restricted to the position shown in the illustratedembodiment, but such elements may also be movably disposed on the mirror10 or 11, whereas to detect the density precisely, the elements shoulddesirably be provided on the slit plate which is near the photosensitivedrum.

FIG. 9 shows another embodiment of the present invention which differsfrom the previously described embodiment in the method of moving thescanning mirrors. The scanning mirrors 10 and 11 are provided on acarriage 120 in an orthogonal relationship with each other. The carriage120 is supported by a support guide bar 122 for pivotal movement aboutan axis 121 which is coincident with the line of intersection betweenthe mirror surfaces of the mirrors 10 and 11, and is movable in thedirections of arrows B and B' along the guide bar 122.

During the reader mode, the scanning mirror 10 is positioned outside theoptical path of the projection lens 5, and during the printer mode, thecarriage 120 is moved in the direction of arrow B and the scanningmirror 10 is positioned in the optical path of the lens 5. After thescanning mirror 10 has been placed at the exposure starting position inthe optical path, the carriage 120 is rotated in the direction of arrowC about the axis 121 while being moved in the direction of arrow B',whereby the entire image to be copied is exposure-scanned on therotating photosensitive drum 12. In this embodiment, the scanningmirrors 10 and 11 can be made more compact. The copying system is notrestricted to the embodiment illustrated, but various known copyingmethods are applicable. The original to be copied is not limited tomicrofilm, but may be a documental original. In the latter case, thereflected light from the documental original may be utilized.

According to the present invention, as described above, the apparatuscan be changed over between the reader mode and the printer mode and theoriginal can be scanned simply by moving the scanning mirrorsrectilinearly so that they are placed into and out of the optical pathof the projection lens and thus, the construction of the apparatus isvery simple and eliminates the necessity of providing any special mirroras well as permitting the use of compact scanning mirrors which in turnleads to the compactness and inexpensiveness of the apparatus. Also, thedensity of the original can be widely detected by at least onelight-receiving element, whereby the image density can be measuredaccurately with a result that copy images of high quality can always beobtained irrespective of the type of the original and the constructionof the apparatus becomes simpler.

Referring now to FIG. 10 which shows another embodiment of the slitunit, reference numeral 216 designates a slit plate provided near thephotosensitive drum 12. The slit plate 216 slidably holds a slit widthvarying plate 220 for varying the width of a slit 215. The slit widthvarying plate 220 is biased in the direction of arrow D by a tensionspring 221 and may be moved in the direction of arrow D' by a solenoid222. A pin 223 secured to the slit plate 216 is fitted in a slot 224formed in the slit width varying plate 220, which is thus movable in thedirections of arrows D and D' by an amount corresponding to the lengthof the slot 224. The solenoid 222 is driven by a signal from amicrocomputer, to be described, to move the slit width varying plate 220in the direction of arrow D', whereby the slit width varying plate 220covers a part of the slit 215 so as to narrow the width of the slit 215and thus reduce the quantity of light passed through the slit 215.

FIG. 11 shows circuitry for controlling the exposure amount by theprocessing of the digital signal of a microcomputer. An image densitysignal obtained by the light-receiving element 219 is amplified by anoutput amplifying circuit 334, whereafter it is applied as input to amultiplexer 336 through a photometric value detecting circuit 335. Onthe other hand, the voltage of a commercial AC power source (AC 100 V)337 is reduced by a transformer 338 and the reduced voltage output (forexample, AC 15 V) thereof is full-wave-rectified by a rectifier circuit339, whereafter the peak value of the source voltage is detected andheld by a peak detector circuit 340 and this peak value is applied asinput to the multiplexer 336. The multiplexer 336 selects an input 1(the photometric value of the detecting circuit 335) or an input 2 (thesource voltage peak value of the detector circuit 340) and supplies itas an analog data to an A/D (analog/digital) converter circuit 341,which converts this analog data into a digital data and supplies thedigital data to a CPU (central processing unit) 345 through an I/O port342. The CPU 345 operationally processes the data of the photometricvalue and the source voltage peak value and supplies a signal to a phasecontrol circuit 346 and a solenoid drive control circuit 347 to providea proper exposure amount to the photosensitive drum 12, and controls thephase angle of the AC wave to the lamp and the width of the slit. Thepower supplied to the illuminating lamp 2 is phase-controlled by abidirectional thyristor (hereinafter referred to as the triac). For thephase control by the microcomputer to be effected, the CPU 345 mustdiscriminate the zero-cross point of the alternating current applied tothe lamp 2 and for this purpose, the voltage of the AC power source 337is reduced by a transformer 350 and the reduced voltage output (forexample, AC 10 V) thereof is waveform-shaped by a zero-cross detectingcircuit 351, is transformed into a signal capable of discriminating thezero-cross point in the CPU 345 and is applied as input to the CPU 345through the I/O port 342.

Reference is now had to FIG. 12 to describe the basic concept of thephase control using the microcomputer used in the present invention. Thezero-cross points (X₁, X₂, X₃, . . . ) of the alternating current (AC100 V) applied to the lamp 2 are discriminated in the CPU 345 by thewaveform applied from the detecting circuit 351 to the CPU 345 and atthis point of time, a timer is set in the CPU 345 and the time-up signalof the timer is put out from the I/O port 342, and in the phase controlcircuit 346, the triac is rendered conductive by this signal, wherebythe phase control of each half wave of the alternating current iscarried out. The set time T of the timer which determines the conductionangle of the triac is controlled by the photometric value of thephotometric value detecting circuit 335 and the peak value of the peakdetector circuit 340, whereby the actually effective power applied tothe lamp 2 is increased or decreased.

The details of the exposure amount control system will now be describedby reference to the flow charts of FIGS. 13 and 14. First, at step 1,the timer for photometry is set to effect phase control so that the lamp2 is turned on with a standard brightness for photometry (which is setto 60% of the 100% brightness when the lamp is used at the ratedvoltage), and at the lamp-on routine of step 2, the lamp 2 is turned onwith the standard brightness. At this time, the width of the slit 215 ispreset to a predetermined condition during photometry. At the lamp-onroutine, the lamp 2 is turned on at a phase determined during the settime of the timer for photometry while the fluctuation of the powersource is being corrected as will later be described. While the lamp 2is turned on at this lamp-on routine, the mirrors 10 and 11 are moved toscan the original and the original is photometrically measured by thelight-receiving element 219 and, at step 3, when the photometry has beenterminated, the lamp 2 is turned off by a photometric operation endsignal from a sequence control microcomputer (not shown). At step 4, bythe signal from the CPU 345, the input 1 is selected in the multiplexer336 and the photometric value from the light-receiving element 219 issupplied to the A/D converter 341, and at step 5, the photometric valueis introduced as a digital data into the CPU 345 through the A/Dconverter circuit. At step 6, the digital-converted photometric value iscompared with a reference value and if the measured value is greater,the program proceeds to steps 7 and 8 whereat a first phase anglecorresponding to the photometric value is calculated, or if the measuredvalue is smaller, the program proceeds to step 9 whereat a second phaseangle corresponding to the photometric value is calculated. Step 6 issuch that whether flicker of the lamp or density irregularity of thecopy image appears with the conduction angle of the triac reduced whenonly the phase angle is controlled on the basis of the photometric valueso that an appropriate lamp brightness is provided is discriminated bycomparing the photometric value with the reference value and when theconduction angle must be reduced, the processing of steps 7 and 8 iscarried out and the exposure amount is appropriately controlled byadjusting the phase angle and the slit width but without reducing theconduction angle and in the other cases, the processing of step 9 iscarried out and the exposure amount is appropriately controlled byadjusting the phase alone. The reference value is suitably preset byexperiment. The CPU 345 stores in the memory therein the relation amongthe photometric value (the density of the original), the proper lampbrightness and the set time of the phase controlling timer, and solvesthis relation on the basis of the photometric value and sets the phasecontrolling timer to the set time corresponding to the solved value, andputs out a phase control pulse when the set time is up, to therebycontrol the phase of the alternating current supplied to the lamp. Atsteps 7 and 9, the phase angle in each photometric value is calculatedand the phase controlling timer is set to obtain the proper lampbrightness. When the photometric value is greater than the referencevalue, at step 7, the timer is set to a set time determined by thecombination with the slit width correspondingly to the photometric valueand at step 8, a solenoid driving signal for narrowing the slit width isdelivered from the CPU 345, and at the lamp-on routine of step 10, thelamp 2 is turned on through the phase control circuit 346 by the phasecontrol pulse put out from the CPU 345 and further, the solenoid 222 isenergized through the solenoid driving circuit 347 to narrow the widthof the slit 215. Thus, an appropriate exposure amount corresponding tothe density of the original is provided to the photosensitive drum 12,the lamp 2 can be used in an appropriate range of brightness and flickerof the lamp or density irregularity of copy image does not occur. On theother hand, when the photometric value is smaller than the referencevalue, at step 9, the timer is set to the set time corresponding to thephotmetric value and the slit 215 is rendered open, and at the lamp-onroutine of step 10, and by the phase control pulse from the CPU 345, thelamp 2 is turned on at a phase angle determined by the set time of thetimer. At step 11, when the exposure termination signal is input fromthe sequence controlling microcomputer at the end of the exposure, themain routine is terminated.

Description will now be made of the lamp-on routine of FIG. 14. First,at step 12, a zero-cross signal is waited for and when the zero-crosssignal is input from the zero-cross detecting circuit 351, the timer isstarted at step 13. At steps 14 and 15, a phase control pulse is put outto the phase control circuit 346 as soon as the time is up, whereby thelamp is turned on at the set phase angle. At step 16, in case of 50 Hz,whether 5 msec. has elapsed from the inputting of the zero-cross signalis discriminated and in case of 60 Hz, whether 4.2 msec. has elapsedfrom the inputting of the zero-cross signal is discriminated. This isfor the purpose of inputting the held source voltage peak value withinthe 1/4 cycle after the peak. At steps 17 and 18, a signal is suppliedto the multiplexer 336 and the input 2 (source voltage peak value) isselected while, at the same time, the source voltage peak value isintroduced as a digital data into the CPU 345 through the A/D convertercircuit 341. At steps 19 and 20, the magnitude of the conduction angleis corrected on the basis of the source voltage peak value so that thebrightness of the lamp is not varied even by a fluctuation of the powersource. Thus, at step 21, the corrected timer is newly set and steps12-21 are repeated until the photometric operation or the exposure isterminated. The calculation of the amount of correction at step 19 iseffected with the relation between the source voltage peak value and theamount of correction stored in the memory within the CPU 345. While, inthe aforedescribed embodiment, the slit width has been varied by onlyone step, design may also be made such that the slit width can be variedby a plurality of steps and the slit width and the phase controlconduction angle are combined to control the exposure amount orcontinuously vary the slit width and the slit width and the phase angleare associated with each other to control the exposure amount.

As described above, by controlling the electric power supplied to thelamp and the stop in combination, the necessity of using the lamp in itsflickering condition is eliminated, whereby copy images free of densityirregularity can be obtained. Also, the lamp can be used in its optimumcondition and therefore, the original can be illuminated by stablebrightness and moreover, the life of the lamp can be lengthened.Further, the exposure amount can be greatly controlled correspondinglyto great variations in the density of the original and the copyingmagnification and particularly, where the original used is a microfilm,the apparatus is used with the copying magnification greatly changed andin such case, a proper exposure amount can be obtained by utilizing thestop without greatly changing the electric power supplied to the lamp,and the exposure amount can be greatly varied for a great fluctuation ofthe copying magnification.

While, in the above-described embodiment, phase control is carried outdigitally by a microcomputer, the phase may also be controlledanalogously. Also, instead of varying the slit width as the system forcontrolling the stop, the stop may be provided between the lamp and theoriginal and the quantity of light passed through this stop may bevaried.

What is claimed is:
 1. A reader-printer in which the image of an original is selectively projected onto a photosensitive medium or a screen, said reader-printer comprising:illumination means for illuminating the original; optical means forming a first optical path for projecting the image of the original which is illuminated by said illumination means onto the screen when said reader-printer is operated in reader mode, and for forming a second optical path for projecting said image onto the photosensitive medium when said reader-printer is operated in printer mode, said optical means comprising a reflecting member for reflecting the light from the original; driving means for moving said reflecting member, said driving means moving said reflecting member to an exposure starting position in the printer mode and thereafter moving it from said exposure starting position to an exposure ending position in order to perform slit exposure; illumination control means for controlling said illumination means from the start of a change from the reader mode to the printer mode, to the start of the exposure of the image onto the photosensitive medium, while causing said illumination means to illuminate the original with a constant quantity of light; photo-detecting means for detecting the light from the original when the original is illuminated with the constant quantity of light in accordance with said illumination control means; and printer control means for controlling the operation of said reader-printer on the basis of an output from said photo-detecting means while causing said reader-printer to form the proper image on the photosensitive medium.
 2. A reader-printer according to claim 1, wherein said reflecting member is moved by said driving means to the exposure starting position in the change of mode from the reader mode to the printer mode, and from said exposure starting position to said exposure ending position in the operation of said reader-printer.
 3. A reader-printer according to claim 2, wherein said illumination control means causes said illumination means to illuminate the original before the movement of said reflecting member starts from said exposure starting position after the change of mode to the printer mode.
 4. A reader-printer according to claim 1, wherein said reflecting member is disposed out of said first optical path in the reader mode and in said first optical path in the printer mode.
 5. A reader-printer according to claim 1, wherein said photo-detecting means detects the light from the original which is reflected by said reflecting member and moves in a direction perpendicular to the moving direction of said reflecting member during the movement of said reflecting member.
 6. A reader-printer according to claim 1, wherein said printer control means controls said illumination means on the basis of an output of said photo-detecting means during the movement of said reflecting member to said exposure ending position.
 7. A reader-printer according to claim 1, wherein the image of the original is projected on said photo-detecting means by the movement of said reflecting member in the printer mode.
 8. A reader-printer according to claim 1, wherein said photo-detecting means is disposed near said second optical path and detects the light from the original reflected by said second mirror.
 9. A reader-printer according to claim 1, wherein said printer control means controls the bias voltage of development means.
 10. A reader-printer according to claim 1, wherein said printer control means controls the light intensity of the exposure which is projected onto the photosensitive medium.
 11. A reader-printer capable of being changed over between a reader mode in which the image on a screen is observed and a printer mode in which the image is reproduced, said reader-printer comprising:a projection lens for .[.selectively imaging the.]. .Iadd.projecting an .Iaddend.image of .[.an.]. .Iadd.the .Iaddend.original on the screen or a photosensitive medium; .[.reflecting means statically located on a first position in the reader mode, and moved in a direction across the optical axis of said projection lens in the printer mode in order to scan the original; a photosensitive medium receiving the light reflected on said reflecting means and moving with a constant speed;.]. .Iadd.first reflecting means opposed to said projection lens and forming a reader optical path for guiding projection light through said projection lens to the screen; second reflecting means being movable into or out of an optical path between said projection lens and said first reflecting means, said second reflecting means, in the reader mode, being placed in a first position which is out of the optical path between said projection lens and said first reflecting means, and in the printer mode, being located in a second position which is in the optical path between said projection lens and said first reflecting means, said second reflecting means when located in the second position forming a printer optical path for guiding the projected light through said projection lens to the photosensitive medium; .Iaddend. driving means moving said .Iadd.second .Iaddend.reflecting means .[.in.]..Iadd., .Iaddend.said .[.direction, said.]. driving means first moving said .Iadd.second .Iaddend.reflecting means toward .[.a.]. .Iadd.the .Iaddend.second position and thereafter moving .[.it.]. .Iadd.said second reflecting means .Iaddend.from the second position to .[.a third.]. .Iadd.the first .Iaddend.position in the printer mode .[., and the image being exposed on the photosensitive medium firing the movement of said reflecting means from the second position to the third position.].; at least one light receiving element .[.on which the light from the original is not projected in the reader mode, and on which the light is projected by the movement of said reflecting means from the first to.]. .Iadd.for detecting the projection light through said projection lens, said at least one light receiving element being arranged in a position where said at least one light receiving element receives light, only when said second reflecting means in located in .Iaddend.the second position; and control means for .[.controlling the operation of said reader-printer on the basis of an output of light receiving element so that the proper reproduction image is formed.]. .Iadd.effecting control so that said at least one light receiving element may detect the projection light during the movement of said second reflecting means from the first position to the second position and so that a proper image may be formed on the photosensitive medium by a signal output from said at least one light receiving element during the movement of said second reflecting means from the second position to the first position.Iaddend..
 12. A reader-printer according to claim 11, wherein said control means controls the light intensity of the exposure which is projected onto the photosensitive medium.
 13. A reader-printer according to claim 11, further comprising a development means, and wherein said control means controls the bias voltage of said development means.
 14. A reader-printer according to claim 11, wherein said light receiving element is moved in a direction intersecting the moving direction of said .Iadd.second .Iaddend.reflecting means during the movement of said .Iadd.first .Iaddend.reflecting means.
 15. A slit exposure type copying apparatus in which the image of an original is projected onto a photosensitive medium so that the photosensitive medium is exposed, said apparatus comprising:a projection lens; a first mirror moving in a direction across the optical axis of said projection lens, for reflecting the light from said projection lens; a second mirror located on the reflection optical path of said first mirror and moving in conjunction with said first mirror, for reflecting the light from said first mirror toward the photosensitive medium; and a slit member located between said second mirror and the photosensitive medium and moving in a direction parallel with the moving direction of said second mirror, wherein the size of the slit remains unchanged during movement of the slit member.
 16. A copying machine according to claim 15, wherein said first and second mirrors are disposed so that their reflection surfaces are perpendicular to each other, and are moved as a unit.
 17. A copying machine according to claim 15, wherein said slit member is moved in conjunction with said mirrors, keeping the width of the slit constant. .[.18. A slit exposure type copying apparatus in which the image of an original is projected onto a photosensitive medium so that the photosensitive medium is exposed, said apparatus comprising:a scanning optical system for scanning an original; driving means for moving said scanning optical system; at least one light receiving element disposed on the optical path of said scanning optical system for receiving the light from the original; means for moving said light receiving element in a direction perpendicular to the scanning direction of said scanning optical system while causing said light receiving element to turn its moving direction at least once while said scanning optical system is scanning the original, wherein said light receiving element detects the density of an image; and control means for controlling said apparatus on the basis of an output of said light receiving element so that a proper image is formed on the photosensitive medium..]. .[.19. A copying machine according to claim 18, wherein said light receiving element is moved in conjunction with said scanning optical system..]. .[.20. A copying machine according to claim 18, wherein said scanning optical system is moved forward and backward, and wherein the image is exposed onto the photosensitive medium during the forward movement of said scanning optical system and the light from the original is detected by said light receiving element during the backward movement of said scanning optical system..]. .[.21. A copying machine according to claim 20, wherein said control means is controlled on the basis of an output of said light receiving element during the backward movement of said scanning optical system..]. .[.22. A copying machine according to claim 18, wherein said light receiving element is moved in said scanning direction while being moved in a direction perpendicular to said scanning direction..]. .[.23. A copying machine according to claim 22, further comprising a member on which said light receiving element is disposed, wherein said member is moved in a direction parallel to said scanning direction, and is moved in said perpendicular direction during the movement of said member in a direction parallel to said scanning direction..]. .[.24. A copying machine according to claim 18, wherein said light receiving element is disposed on said slit plate..]. .[.25. A slit exposure type copying apparatus in which the image of an original is projected onto a photosensitive medium so that the photosensitive medium is exposed, said apparatus comprising: a scanning optical system for scanning an original; driving means for moving said scanning optical system; at least one light receiving element for receiving the light from the original; movable supporting means for supporting said light receiving element wherein said supporting means moves in a direction parallel to the moving direction of said scanning optical system; means for moving said light receiving element in a direction perpendicular to the moving direction of said supporting means while causing said light receiving element to turn its moving direction at least once during the movement of said supporting means, wherein said light receiving element detects the density of an image; and control means for controlling said copying apparatus on the basis of an output of said light receiving element so that the proper image is formed on the photosensitive medium..].
 26. A reader-printer capable of being changed over between a reader mode in which an image of an original is projected onto a screen and a printer mode in which the image is projected onto a photosensitive medium, comprising:illumination means for illuminating the original; .[.reflecting means statically located in the reader mode, and moved in a direction across the optical axis of a projection lens in the printer mode in order to expose the image onto the photosensitive medium by scanning so as to reflect the light from the original toward the photosensitive medium; and.]. .Iadd.a projection lens; a first mirror for forming a reader optical path guiding a projection light through said projection lens onto the screen; a second mirror displaceable in a direction across the optical path of said projection lens, said second mirror being movable in between said projection lens and said first mirror and out therefrom; a third mirror displaceable in the same direction as said second mirror and arranged at a predetermined angle with respect to said second mirror, said second and third mirrors forming a printer optical path guiding the projection light through said projection lens to the photosensitive medium; driving means for moving said second and third mirrors between a receded position and a scanning starting position in the printer mode; .Iaddend. at least one light receiving element .[.for receiving the light from the original to control the light intensity of the illumination means on the basis of the received light amount, said reflecting means being moved in said direction in the printer mode before the image is projected onto the photosensitive medium, so as to form an optical path for projecting the image onto said light receiving element..]..Iadd.arranged in a position in which, when said second mirror has been moved in the optical path between said projection lens and said first mirror, the projection light through said projection lens can be detected; and control means for detecting the projection light by said at least one light receiving element during the movement of said second and third mirrors from the receded positions to said respective scanning starting positions, and controlling said illumination means during the movement of said second and third mirrors from their respective scanning starting positions to their receded positions, on the basis of the signal output from said at least one light receiving element, the image of the original being exposed to the photosensitive medium during the movement of said second and third mirrors from their respective scanning starting positions to their receded positions. .Iaddend.
 27. A reader-printer capable of being changed over between a reader mode in which an image of an original is projected onto a screen and a printer mode in which the image is projected onto a photosensitive medium, and is developed by development means which utilizes a developing bias voltage comprising:illumination means for illuminating the original; .[.reflecting means statically located in the reader mode, and moved in a direction across the optical axis of a projection lens in the printer mode in order to expose the image onto the photosensitive medium by scanning so as to reflect the light from the original toward the photosensitive medium; and.]. .Iadd.a projection lens; a first mirror for forming a reader optical path guiding a projection light through said projection lens onto the screen; a second mirror displaceable in a direction across the optical path of said projection lens, said second mirror being movable in between said projection lens and said first mirror and out therefrom; a third mirror movable in the same direction as said second mirror and disposed at a predetermined angle with respect to said second mirror, said second and third mirrors forming a printer optical path guiding the projection light through said projection lens to the photosensitive medium; driving means for moving said second and third mirrors between a receded position and a scanning starting position in the printer mode; .Iaddend. at least one light receiving element .Iadd.arranged in a position in which, when said second mirror has been moved in the optical path between said projection lens and said first mirror, the projection light through said projection lens can be detected; and .Iaddend. .[.for receiving the light from the original to control the development bias voltage of the development means, on the basis of the received light amount, said reflecting means being moved in said direction in the printer mode before the image is projected onto the photosensitive medium, so as to form an optical path for projecting the image onto said light receiving element.]. .Iadd.control means for detecting the projection light by said at least one light receiving element during the movement of said second and third mirrors from the receded positions to the respective scanning starting positions, and controlling the developing bias voltage during the movement of said second and third mirrors from the scanning starting positions to the receded positions, on the basis of a signal output from said at least one light receiving element, the image of the original being exposed to the photosensitive medium during the movement of said second and third mirrors from the scanning starting positions to the receded positions.Iaddend.. 